1. Field of the Invention
The present invention generally relates to motor vehicle power train assemblies. More specifically, the present invention relates to a power train assembly having a power transfer unit located prior to a final drive unit.
2. Description of the Prior Art
Historically, automobiles in the United States have primarily utilized a rear wheel drive power delivery schemes. In adapting these rear wheel drive schemes into four wheel drive applications, a transfer case was, and often still is, positioned at the output of the transmission assembly. When engaged, the transfer case diverts a portion of the power coming from the transmission assembly from the rear wheels to the front wheels.
Today, a significant portion of new automobiles in the United States, and perhaps the world, are front wheel drive based vehicles. In a typical front wheel drive vehicle, typically both the engine and the transmission assembly are transversely oriented relative to the vehicle. By positioning the engine and transmission assembly transversely in the vehicle, a more direct coupling of the transmission assembly to the vehicle""s transaxle and front wheels is achieved. In doing so, the final drive unit (where the last torque multiplication takes place) and the front wheel differential are often incorporated directly into the transmission assembly itself.
With front wheel drive vehicles themselves becoming a mature market, a recent trend in the automobile industry has been to adapt front wheel drive schemes for all or four wheel drive applications. This is accomplished by providing a power transfer unit that diverts a portion of the power from the front wheels to a rear wheel drive shaft and, subsequently, the rear wheels.
Seen in FIGS. 1a and 1b is a typical prior art power transfer unit 10. The power transfer unit 10 includes a housing 12 within which is located a gear set 14 comprised of a parallel gear set 16 and a non-parallel gear set 18. The parallel gear set 16 includes a cylindrical extension 20 that operates as its input and this input 20 is coupled to the transversely oriented output 22 of the transmission assembly by way of a splined engagement 24. The cylindrical extension 20 itself is an extension off of a gear wheel 26 or may be a sleeve to which the gear wheel 26 mounts. From the gear wheel 26, power is transferred through a second and third gear wheel, respectively 32 and 34. These gear wheels 32 and 34 are each supported on bearings 36 for rotation about axes 38 and 40 that are parallel to the rotational axis 28 of the first gear wheel 26.
The non-parallel gear set 18 includes a bevel ring gear 44 that is mounted to a shaft or sleeve 42 onto which the third wheel gear 34 is mounted or formed therewith. The bevel ring gear 44 engages a bevel gear 46 mounted to another shaft 48 whose axis is generally perpendicular (and therefore non-parallel) to that of shaft 42. Mounted to an opposing end of the shaft 48 is an output member 50, illustrated as including a flange 52 and appropriately located bolt openings 54. The latter features enable the output member 50 to be bolted to a rear drive shaft (not shown).
As seen in FIG. 1a, the line 56 along which the gear wheels 26, 32 and 34 of the parallel gear set 16 engage with one another generally corresponds with the axis about which the output member 50 rotates. When locating of the power transfer unit 10 relative to the output of the transmission 22, it is clear that this line 56 may be offset from the centerline of the vehicle. Additionally and as seen in FIG. 1b, the axis 28 of input into the power transfer unit 10, is offset, vertically or elevationally in the vehicle, relative to the output axis 58 about which the output member 50 rotates. This xe2x80x9cdropxe2x80x9d or height decrease from the transmission assembly output 22 to the output member 50 results from the relative positioning of the first, second and third helical gears 26, 32 and 34 of the parallel gear set 16, in conjunction with the non-parallel gear set 18. The non-parallel gear set 18 is a hypoid beveled gear set where the axis of rotation 40 of the bevel ring gear 44 does not intersect the axis 58 of rotation of the bevel gear 46.
Located within the transmission assembly, and before the output 22 thereof, is a final drive unit (illustrated schematically as box 57). The final drive unit 57 performs the last torque multiplication in the power train and is configured in any one of a number of conventional constructions well known in the art. One such construction is a planetary gear set with the input to the final drive unit being through a sun gear while the output of the final drive assembly is through a ring gear. The ring gear may be directly coupled to the transmission output 22 and therefore a large amount of torque is delivered to the power transfer unit.
Since the power transfer unit receives power after the final drive assembly 57, the components of the power transfer unit 10 must be robust enough for high torque loads to pass there through. This adds weight and expense to the power transfer unit.
In view of the above and other limitations on the prior art, it is an object of the present invention to provide a drive train construction that permits a decrease in the weight of the system. In doing so, the present invention provides a power transfer unit located in the power train assembly prior to torque multiplication by the first drive unit.
The present invention overcomes the limitations of the prior art by packaging the power transfer unit such that it receives power from the transmission assembly before torque multiplication by the final drive unit. The present invention may therefore be seen as a power transfer unit that includes a parallel gear set that receives its input from an intermediate output of the transmission assembly. The power transfer unit includes a parallel gear set, more specifically a drive sprocket wheel that transfers rotation to an output sprocket wheel through either an intermediate transfer wheel, a transfer chain or belt. The output sprocket wheel is mounted axis is generally parallel to the axis about which the drive sprocket wheel rotates the output axis of the transmission assembly. That shaft then transfers power to a non-parallel gear set.
In the non-parallel gear set, a hypoid bevel gear is mounted to or coaxial with the same shaft as the output sprocket wheel so as to rotate therewith. The hypoid bevel gear engages a hypoid pinion gear mounted to a second shaft, this second shaft being oriented generally perpendicularly to the first shaft. On the distal end of the second shaft is the output member of the power transfer unit. This output member couples the power transfer unit to the rear drive shaft of the vehicle.
In another aspect, the present invention uses a power transfer unit, coupled to an output of the transmission assembly before the final drive unit, with a non-parallel gear set being coupled to the output of the transmission assembly. The output of the non-parallel gears set is then used as the input into a parallel gear set, if desired or required. Subsequent to the input of the power transfer unit, the output of the transmission assembly is also provided to a final drive unit. Final torque multiplication takes place in the final drive unit, which may be a planetary gear set using its sun gear as the input. From the final drive unit, power is supplied to a front differential and thereafter to the front wheels of the vehicle.
By incorporating the power transfer unit on the front transaxle before the final drive unit, the power transfer unit is subjected to less torque and can be smaller, lighter and simpler in design.
In one aspect, the present invention is therefore seen to be a drive train having a power transfer unit adapted to connect to an intermediate output portion of a transmission assembly in a primary drive line, with the power transfer unit also being coupled to a secondary drive line.
Additional objects and features of the present invention will be readily apparent to those skilled in the art from a review of the attached drawings, the following detailed description and the appended claims.